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Green spotted are a brackish fish I believe, they can survive in salt but not as long. I don't know how they compare to regular salt water puffers, but maybe consider a single saddle valentini puffer instead?
Have a look on liveaquaria.com
sea apples are considered expert only and it says that any fish that is considered reef safe with caution may eat it (that includes puffers)
There is plenty of good info on fish types and compatibility though...
I have found that whether they are well fed or not it doesn't matter. In my experience my puffer didn't get the taste for corals until he matured a bit, after about a year...